Recently, there has been an increasing demand for digital content distribution services making use of communications or broadcasting.
For example, music distribution services have now started to be provided, such as one in which music data is downloaded to a cellular phone to be stored into a storage medium connected thereto, and the music data is played back on the cellular phone or other playback device whenever it is demanded. In addition, other than music data, a distribution service for video data such as a movie, etc., or document data such as newspaper accounts, etc., has also been conceived.
In a system which distributes content electronically, it is an important issue how to prevent unauthorized use of stored content or unauthorized copying thereof from occurring for the protection of a right of a copyright holder. Though it goes without saying that it is necessary to provide a scheme which eliminates the risk of unauthorized copying or tampering, especially, these days, there has been a growing importance of a freer content use control scheme which also controls number of times of content viewing.
As a conventional digital content use control scheme, the invention described in Japanese Laid-Open Patent Publication No. 2000-315177 (hereafter referred to as the conventional scheme) is known.
An explanation is given below on the outline of the conventional scheme. The conventional scheme is a content management method for restricting the number of content copies copied into storage media, where an allowed number of copies k is set for each of content, and a restriction is imposed on the copying of content so that the number of storage media in which the content is copied does not exceed k at the same time.
FIG. 1 illustrates a conceptual diagram of a content use model according to the conventional scheme where k=3. A content use management system (PC) stores the allowed number of copiable content for each of content and identification information of storage media where copied content are stored (as an accommodation book). Upon reception of instructions for copying and storing of distributed content into a storage medium, a copied content is stored into the storage medium in a case where there is a remaining balance in the allowed number of copiable content for this content. At such an occasion, each time a copied content is stored into storage medium, the allowed number of copiable content is decremented by one (check-out).
In addition, upon the reception of instructions for erasing of copied content from the storage medium, the copied content is erased from the storage medium, and the allowed number of copiable content is incremented by one at each time of erasing a copied content (check-in). At such an occasion, only in a case where the identification information of the storage medium is stored in the “accommodation book”, the copied content is erased from the storage medium.
In an example of FIG. 1, because a predetermined allowed number of copiable content k for content is “3”, it is possible to perform checkouts to three storage media at the maximum at the same time. Furthermore, the allowed number of copiable content is incremented by one by checking in checked-out content, therefore it is possible to perform a checkout to another storage medium.
In addition, in this content use model, content which is checked out to a storage medium is unable to be checked into another content use management system other than the original content use management system from which the content is checked out.
In this way, according to this system, it is possible to impose strict limitations on copied content through management of check-ins and checkouts.
However, it is often that a content use management scheme by means of check-ins and checkouts, especially its concept of check-in, is hard for users to become familiar with it, ending up being a cause of a hindrance to making content distribution services popular.
Moreover, according to a check-in/checkout scheme, it is difficult to embody a control mode which restricts the viewing count of content, etc., by affixing use restriction information which prescribes the allowed playback count of the content, etc., to the content. For example, in a case where a checkout to a storage medium is performed with use restriction information which restricts the allowed playback count of content affixed thereto, the following problem would arise.
By playing back copied content in a storage medium, the allowed playback count of the content decreases, meanwhile, by playing the content back, the allowed playback count at a content use management system side also varies in accordance with its number of times of playbacks. In this way, due to the difference in the number of times of playbacks after checkout, there is a discrepancy between the value of the allowed playback count of the content at the content use management system side and the value of the allowed playback count of the content at the storage medium side. For this reason, there arises a problem regarding which value the allowed playback count should be adjusted to when checking content at the storage medium side in. In addition, regardless of which value it is adjusted to, it is inevitable that such a content use model would be far harder one to be understood by users, as well as the greater complexity in processing on equipment.